> You can't just say "No". You need to say "No, these are the reasons why, and here are my solutions". It's too easy sitting back and pooh-poohing every idea, and there are a lot of people that love doing that. Coming up with solutions is the right way to approach it, because people really don't like hearing "No".
Because people don't like hearing "No", its even better to not only come up with solutions, but then also to present them in the context of "Yes, we should do what you are suggesting, with these refinements" rather than "No, instead of doing what you are suggesting, we should use this alternative".
The substance is the same, of course, but it provides acknowledgement and validation to the person making the proposal rather than dismissal and rejection. This can make a very big difference in how people respond.
"Yes, we should do what you are suggesting, with these refinements"
That would only work if the proposed solution was somewhat close to being viable. But if the only way to succeed is to throw the existing solution out and start from scratch, it's hard to find a diplomatic way of saying so.
What I find usually works is working back from the proposed implementation to the goal that it is supposed to serve. You can usually do this in a validating rather than rejecting way. Once you've identified and validated the goal you can address cover a with the proposed approach and present alternatives without the proposer viewing it as a rejection since you got to common ground on what you are trying to achieve before proposing alternatives.
Often the problem with an initial "no" to a proposal is that the proposer identifies the proposal tightly with the purpose and suggesting an alternative to the proposal without validating the goal reads as rejection of the goal.
Because people don't like hearing "No", its even better to not only come up with solutions, but then also to present them in the context of "Yes, we should do what you are suggesting, with these refinements" rather than "No, instead of doing what you are suggesting, we should use this alternative".
The substance is the same, of course, but it provides acknowledgement and validation to the person making the proposal rather than dismissal and rejection. This can make a very big difference in how people respond.